Migrate to SLF4J from Log4J
In this guide, we'll use OpenRewrite to perform an automated migration from Apache Log4j
(handling both log4j 1.x
or log4j 2.x
) to the Simple Logging Facade for Java (SLF4J
).
Example Configuration
See various ways you can configure your project to run this recipe on the recipe reference page. This is also where you can find the full list of changes it will make.
Once you've configured your project, you're ready to execute the migration by running mvn rewrite:run
or gradlew rewriteRun
. After running the migration you can inspect the results with git diff
(or equivalent), manually fix anything that wasn't able to be migrated automatically, and commit the results.
Before and After
Similar to the SLF4J Migrator
, the goal of the Log4jToSlf4j
recipe is to significantly reduce the amount of work involved in migrating Log4j
to SLF4J
. Because OpenRewrite works by leveraging type-attributed Lossless Semantic Tree (LST) representing your source code, the Log4jToSlf4j
recipe can overcome several limitations discussed in the SLF4J Migrator
guide.
.toString()
.toString()
Because Log4j
logging statements are automatically migrated to use the SLF4J Parameterized Logging
equivalent (see "Use SLF4J Parameterized Logging"), messages of type String
are supported. Therefore, there is no need to add a .toString()
method invocation on the object.
FATAL
to ERROR
FATAL
to ERROR
The Log4j
log level FATAL
is not supported in SLF4J
. Therefore, FATAL
level log statements are migrated to ERROR
level.
Migrate using type
information
type
informationA method declaring multiple loggers on the same line will have a complete conversion.
Handle Exception
Migrations
Exception
MigrationsAdditionally, Log4j
ERROR
log level exceptions are migrated to their SLF4J
equivalent:
For the full list of changes, see the recipe's reference documentation.
Known Limitations
The following is a list of known limitations/issues:
Currently,
log4j
properties and configuration files are not migrated.Log4j
configuration customizations which do not have anSLF4J
equivalent cannot be migrated.
We are always looking for feedback on which tasks should be prioritized. If you have a specific use case that is not yet covered by this project, please reach out to our team or submit a PR to help out the community.
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